Genital herpes vaccine candidate promising in phase II

Genocea Biosciences’ GEN-003 found to reduce recurrence
and transmission of the virus

A vaccine that could free patients with genital herpes from lifelong drug treatment to control outbreaks has shown promise in a phase II trial.

The vaccine - called GEN-003 and developed by Genocea Biosciences - is a T cell-enabled therapeutic vaccine designed to reduce the duration and severity of clinical symptoms associated with genital herpes and control transmission of the causative organism Herpes simplex virus type 2 (HSV-2).

At the moment, there is no vaccine available for HSV-2, which affects an estimated 400m people worldwide between the ages of 15 and 49. If approved, GEN-003 would be the first therapeutic vaccine to address genital herpes - or indeed any infectious disease - and Genocoa has previously predicted that it could become a $1bn product if brought to market.

Genital herpes is a recurrent, lifelong viral infection and while symptoms can be managed with antiviral drugs such as valaciclovir or famciclovir, patients tend to suffer recurrent outbreaks, in some cases several times a year. HSV is spread when patients have symptoms, so a key goal is to prevent outbreaks occurring.

However, efforts to develop an effective vaccine for HSV-2 have resulted in a string of failures. Last year, Vical reported that two versions of its experimental vaccine failed to show efficacy in a phase III trial, while in 2012 GlaxoSmithKline dropped its Simplirix candidate on disappointing data.

In the phase II trial reported at the American Academy of Dermatology (AAD) in Washington DC this week, 310 patients with HSV-2 infection were treated with placebo or three doses of the GEN-003 vaccine (at varying doses) given three weeks apart.

After the six months follow-up, there was an average 58% reduction in viral shedding. According to Zeena Nawas of the Center for Clinical Studies in Houston, Texas, who presented the results at the AAD meeting, this was a clinically relevant reduction and should reduce transmission of the virus.

At the six-month time point all the participants in the study reported reductions in lesions - including those in the placebo group - and it was not possible to show a difference between the vaccine and control. Reductions ranged from 43% to 69%, according to the presentation.

Nevertheless, the investigators suggest that a difference between the vaccine and placebo may become apparent at a later time point; 12-month data is due for publication in the coming weeks. Meanwhile, virologic and clinical efficacy data from a phase IIb study is expected in the middle and second half of 2016, respectively.

Analysts responded positively to news of the phase II data presented at the AAD meeting, with UBS and Citigroup both starting coverage of the company with a 'buy' rating.

Other companies working on HSV-2 vaccines include Sanofi/Immune Design, Agenus, Tomegavax and Australian company Admedus, which has also just reported preliminary phase II data on its candidate.

Data from the first 20 patients enrolled into the 44-patient study revealed a 90% reduction in monthly disease outbreaks and a reduction in average number of days HSV-2 was detected in patients compared to baseline. The trial is due to complete later this year.